When a vehicle with a low vehicle height (hereinafter referred to as a small vehicle) such as a passenger car collides head-on with or rear-ends a vehicle with a high vehicle height (hereinafter referred to as a large-sized vehicle) such as a truck, the small vehicle may go under the bottom of the large-sized vehicle. In order to prevent such an inconvenience, it has been known that the large-sized vehicle has an underrun protector provided at its front or rear. Examples of an underrun protector mounting structure of the vehicle including the underrun protector described above include those disclosed in Patent Documents 1 to 3.
According to the underrun protector mounting structure of a vehicle disclosed in Patent Document 1 described above, since a protector main body has a closed cross-section structure, high rigidity and strength can be secured. Moreover, a connection portion of the protector main body and a mounting base (the portion on which the largest bending moment acts) is reinforced by a stiffener disposed inside of the protector main body. Thus, rigidity and strength required for the protector main body against the bending moment can be secured.
According to the underrun protector mounting structure of a vehicle disclosed in Patent Document 2 described above, an impact load caused by collision can be effectively absorbed by rigidity and flexibility of a thin-walled steel pipe that forms a protector and of a reinforcing pipe to be inserted into the thin-walled steel pipe.
According to the underrun protector mounting structure of a vehicle disclosed in Patent Document 3 described above, an underrun protector is connected to a supporting arm fixed to a vehicle body frame through a connection member. This connection member has a main body part, connected to the supporting arm, with an approximately squared U-shaped cross-section, and flange parts which are extended, while facing each other, in a lateral direction of the vehicle from ends of the main body part and which are connected to the underrun protector. Thus, a thickness of the underrun protector is substantially increased by connection of the flange parts of the connection member. Therefore, rigidity and strength of the underrun protector are improved.
Patent Document 1: Japanese Patent Application Publication No. 2003-276536
Patent Document 2: Japanese Patent Application Publication No. 2003-312404
Patent Document 3: Japanese Patent Application Publication No. 2004-175306